1. Field of the Invention
The invention relates to improved intraosseous injection system and, more particularly, to a strengthened intraosseous needle with positioning gauge and a penetration limiting stop to obtain precise delivery of an anesthetic to the most effective site, in a patient's mouth, and reduce the pain associated with endodontic treatment.
2. Description of the Background
The administration of anesthetics is an important part of dentistry. The effective reduction of pain makes a patient comfortable and allows the dentist to operate with confidence. Pain control is more difficult when a diseased nerve is causing acute pain before the treatment has begun. This is often the situation in endodontic (root canal) therapy. Known injection techniques are typically used to achieve pulpal anesthesia, which normally alleviates the pain from the diseased nerve and allows the dentist to complete therapy without complications from excessive pain. However, there are situations where these known techniques are insufficient because either the patient has a low threshold for pain or for some other reason the anesthetic is not sufficiently effective to reduce the pain.
Usually, an anesthetic is injected into the lingual aspect of the mandibular ramus, using conduction anesthesia (the mandibular block). Due to variations in human bone structure, the effectiveness of this procedure depends, in part, on the location of the affected tooth. Mandibular block anesthesia is more likely to fail when the disease is present in a mandibular tooth as opposed to a maxillary tooth. The reduced failure rate in the maxilla is due to the thin cortical plate of the maxilla. The cortex of the mandible is much thicker. A study by Walton and Abbott showed incomplete anesthesia in 32% of maxillary teeth and 66% in mandibular teeth (Walton, R. and Abbott, B. “Periodontal Ligament Injection: A Clinical Evaluation”, Journal of the American Dental Association, 1981; 103:571). A separate study by Malamad found that mandibular teeth were not effectively anesthetized 91% of the time (Malamad, S. “Teeth Requiring Supplemental Injections, [unpublished data] 1997). Infiltration anesthesia can be used for the maxilla and effectiveness will be achieved 90% of the time.
In any case, a supplemental injection is necessary when the mandibular block or infiltration fails to sufficiently anesthetize the site of the disease. Known means of supplying supplemental injections of an anesthetic are by periodontal ligament injection and intraosseous injection. When the mandibular block or infiltration anesthesia is not sufficiently effective, the periodontal ligament injection is usually the next choice. This injection is usually given with a device that improves the mechanical advantage over that of an ordinary syringe, known as the ligamental gun syringe, with an extra short, 30 gauge needle. The bevel of the needle is placed against the root of the tooth while it is advanced down along the gingival pocket into the periodontal ligament space until resistance is met. The anesthetic is delivered to this location. This process suffers from having a short effective period of the anesthesia and the process poses a risk of osteomyelitis.
The other choice is intraosseous injection, by which local anesthetic is injected directly into the cancellous bone of the alveolar process surrounding the root of the targeted tooth. This method is ideally suited to treatment of mandibular teeth because it provides for perforation of the thick mandibular cortex, prior to injection of the anesthetic. Generally, at some position immediately adjacent the affected tooth a small perforation is made in the cortex of the alveolar process at a location which will allow the anesthetic to be delivered into the inner compartment composed of spongiosa or medullary (cancellous) bone. If the perforation is correctly located, the patient feels immediate relief from pain and, depending on the location of the perforation and the quantity of anesthetic delivered, the anesthesia may affect one or several teeth, as needed.
The effectiveness of the intraosseous injection was reported in the following study: Nustein, J., Reader, A., and Nist, R., “Anesthetic Efficacy of the Supplemental Intraosseous Injection of 2% Lidocaine with 1:100,000 Epinephrine in Irreversible Pulpitis”, Journal of Endodontics, (1998, 24:287). The Nustein et al. study included data showing that 81% of mandibular teeth required intraosseous anesthesia due to the irreversible pulpitis present and failure of the traditional mandibular block. Regarding maxillary teeth, the data showed that the intraosseous injection was required in 12% of the teeth. Overall the intraosseous injection was successful in 88% of the cases, thereby achieving the pulpal anesthesia necessary for endodontic treatment. A similar study (Parente, S., Anderson, R., Herman, W. “Anesthetic Efficacy of the Supplemental Intraosseous Injection for Teeth with Irreversible Pulpitis”, Journal of Endodontics, (1998, 24:826)) revealed a 91% success rate of intraosseous injections thus allowing endodontic therapy.
Types of intraosseous injections vary. One form of intraosseous injection is the Stabident System by Fairfax, Dental, Inc. (See http://www.stabident.com/delivery-systems-described-regular.html citing U.S. Pat. Nos. 5,057,013 and 5,173,050 to Dillon issued on Oct. 15, 1991 and Dec. 22, 1992, respectively, for a “Dental Cortical Plate Perforator”), which uses a two-step perforation and injection process. This Stabident two-step procedure is referenced in the Parente study, supra, as well as an article by Ronald Brown, DDS, MS, “Intraosseous Anesthesia: A Review”, Journal of the California Dental Association, (October 1999). Specifically, the Stabident System consists of using a perforator (0.9 mm long with a 0.43 mm diameter) to drill hole in the cortical plate of the alveolar process and a separate injection needle (27 gauge) to inject the anesthetic into the cancellous bone within. The injection needle attaches to a separate standard syringe. Kits are available with injection needles modified such that the bevel at the end of the needle has a blunted tip. Generally, the site of a lateral injection for this system is a point about 2 mm apical to the intersection of a horizontal line along the gingival margins of the teeth and a vertical line through the interdental papilla. Unfortunately, this two-step Stabident process presents a risk of damaging the bone while drilling and a risk of drilling into the root surface of the tooth. In addition to the risk of injury to the patient, bleeding and clotting at the drilling site impair the view of the drill point, making precise drilling more difficult and obscuring the opening during the second step of injecting the anesthetic. Furthermore, in a case of periodontal gingival disease, a drill hole cannot be made in the area to be injected.
An improvement over the two-step intraosseous injection process is described in U.S. Pat. No. 3,976,070 to Dumont, issued on Aug. 24, 1976, which claims a support device for a small gauge hypodermic needle that allows the injection to be completed in a one-step process. The support device includes a funnel-like structure adapted to fit over the base of the hypodermic needle and a siding tip guard adapted to slide coaxially inside the funnel-like structure in the manner of an expansible telescope. At the end of the tip guard, away from the funnel-like structure, there is an enlarged hub adapted to press against the gum in the mouth of the patient and through which the hypodermic needle is inserted, through the gum and into the bony structure below. This one-step intraosseous needle eliminates the problems associated with the two-step process. The small size of the needle reduces the risk of damage to the bone and the underlying tooth, even if the site for the injection is not accurately located. The proper location for the injection is visually selected at a approximately 1 mm above the alveolar crest of a maxillary tooth or 1 mm below the aveolar crest of a mandibular tooth.
As discussed above, the primary advantage of intraosseous injections is the targeted administration of a local anesthetic to one or several particular teeth. While a slight miscalculation of the perforation and injection site when using the Dumont '070 system will not result in damage to the bone or underlying tooth, it will likely make the anesthetic ineffective on the area where it is needed. Therefore, correct positioning of the needle for perforation and injection is crucial. Traditionally, the needle is position at the site of injection by viewing the area and simply estimating the correct insertion point. In order for the anesthetic to be effective using the system disclosed in the Dumont '070 patent, the needle must perforate the cortex approximately 1 mm from the aveolar crest, as described above. However, even if the correct perforation location is selected, the needle may bend, buckle, and/or slide along the cortex rather than penetrating the precise selected location. This bending and/or sliding of the needle may cause a distorted infusion of the anesthetic and an ineffective injection.
In order for the injection to be most effective, the anesthetic must be delivered to the cancellous bone of the alveolar process adjacent the affected root. As described above, the needle must be inserted through the outer cortical plate into this cancellous bone. The needle should not penetrate beyond the cancellous bone through the inner cortical plate or alveolar bone into the root of the tooth. Again, the proper depth for the site of the injection is estimated by viewing the area where the injection is to be made. This “by sight” method of aligning the syringe with the targeted injection site and for determining the depth of the injection is not as precise as it should be given the resultant ineffectiveness of the anesthetic if an error does occur.
Thus, there is a need for an improved one-step intraosseous injection system. It would be advantageous over the prior art if the system was configured for attachment to a standard syringe. It would also be advantageous if the system simply and economically reinforced and stabilized the injection needle during bone penetration, promoted accurate targeting of injections, and included a means for limiting the depth of injection needle penetration. Specifically, it would be advantageous over the prior art to: (1) configure a intraosseous injection needle for attachment onto a standard syringe (i.e. a dental anesthetic syringe having a short high tensile strength needle); (2) provide the injection needle with a protective sliding cannula and sleeve to prevent bending and sliding of the injection needle during penetration of cortical bone (i.e. the outer cortical plate of the alveolar process); (3) attach a sight/gauge to the sleeve for targeting the precise position of penetration and insertion of the injection needle into the bone (i.e. the alveolar process); and, (4) incorporate a cannula stop in the sleeve which effectively limits penetration of the injection needle, ensuring delivery of the injected substance to the targeted location (i.e. cancellous bone).